Research On Tungsten, Molybdate Fluorescent Material By Molten Salt Synthesis Method

Rare earth doped fluorescent materials are widely used in lighting, display devices, sensors, high-energy physics, biomedical and other fields. The red phosphors AMoO₄:Eu³⁺, Li⁺(A=Ca, Sr), EuLiM₂O₈(W =Mo, W), Y₂O₃:Eu³⁺ and the yellow white LED phosphor Y₃Al₅O₁₂:Ce³⁺(YAG:Ce) synthesized by molten salt method can be effectively excited by ultraviolet light or blue light and emit fluorescence with high intensity.. The growth of fluorescent material crystals in molten salt can be controlled by adjusting the type and the amount of molten salts, reaction temperature and reaction time. The influence of experimental conditions on composition, morphology and luminescence properties of samples has been investigated by XRD, SEM, excitation and emission spectra. Specific conclusions are as follows:1. In molten salt environment, octahedral particles AMoO₄:Eu³⁺, Li⁺(A=Ca, Sr) and EuLiM₂O₈(W=Mo, W), fibrous SrMoO₄:Eu³⁺, Li⁺, rod EuLiM₂O₈(W=Mo, W), spherical Y₂O₃:Eu³⁺ and spherical YAG phosphors have been successfully synthesized.2. Octahedral shape of phosphor crystals have been obtained in NaCl at 800°C, fibrous and rod-like phosphor crystals have been prepared in KCl respectively at 900°C and 800°C. Spherical Y₂O₃:Eu³⁺ particles have been fabricated in Li₂SO₄ at 1100°C. Globular YAG:Ce³⁺ crystals have been obtained in KCl with K3PO4 as a additive at 1200°C. With the temperature and molten salt content increasing, the morphology of tungsten molybdate phosphors has changed to be irregular flakes. 3. It is observed that the fluorescence intensity of CaMoO₄:Eu³⁺, Li⁺ decreases with the increase of the reaction temperature. It is supposed that it is difficult for Eu³⁺ to enter the lattice of host CaMoO₄ at high temperature. Therefore, the characteristic emission of Eu³⁺ decreases whereas the intrinsic emission of molybdate calcium increases. In EuLiM₂O₈ phosphor system, the luminous intensity of rod-shaped samples is higher than that of octahedral samples. In Y₂O₃:Eu³⁺ system, the brightness of the samples obtained in sulfate is higher than that in chloride. The sample Y₂O₃:Eu³⁺ synthesized in Li₂SO₄ shows the highest brightness compared to those synthesized in other molten salts. As for the YAG:Ce phosphor, the sample with homogeneous morphology obtained in the complex molten salt of NaCl and KCl has higher brightness than that synthesized in single molten salt.